diff options
| author | H. Peter Anvin <hpa@zytor.com> | 2008-01-30 13:33:01 +0100 |
|---|---|---|
| committer | Ingo Molnar <mingo@elte.hu> | 2008-01-30 13:33:01 +0100 |
| commit | c4d9ba6da9f050ebb7e0d70769e3dca0fd45334f (patch) | |
| tree | 03c771875a9cf2cc2026066f8a686cf53f0739f4 | |
| parent | 2a6648e65a2939b80c44262975176a15bac3a75e (diff) | |
x86 setup: make PM transition more paranoid; cleanup 32-bit entry
Make the transition to protected mode more paranoid by having
back-to-back near jump (to synchronize the 386/486 prefetch queue) and
far jump (to set up the code segment.)
While we're at it, zero as many registers as practical (for future
expandability of the 32-bit entry interface) and enter 32-bit mode
with a valid stack. Note that the 32-bit code cannot rely on this
stack, or we'll break all other existing users of the 32-bit
entrypoint, but it may make debugging hacks easier to write.
Signed-off-by: H. Peter Anvin <hpa@zytor.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
| -rw-r--r-- | arch/x86/boot/pmjump.S | 44 |
1 files changed, 32 insertions, 12 deletions
diff --git a/arch/x86/boot/pmjump.S b/arch/x86/boot/pmjump.S index fa6bed1fac1..ef0da1f2c7f 100644 --- a/arch/x86/boot/pmjump.S +++ b/arch/x86/boot/pmjump.S @@ -29,12 +29,13 @@ */ protected_mode_jump: movl %edx, %esi # Pointer to boot_params table - movl %eax, 2f # Patch ljmpl instruction + + xorl %ebx, %ebx + movw %cs, %bx + shll $4, %ebx + addl %ebx, 2f movw $__BOOT_DS, %cx - xorl %ebx, %ebx # Per the 32-bit boot protocol - xorl %ebp, %ebp # Per the 32-bit boot protocol - xorl %edi, %edi # Per the 32-bit boot protocol movl %cr0, %edx orb $1, %dl # Protected mode (PE) bit @@ -42,15 +43,34 @@ protected_mode_jump: jmp 1f # Short jump to serialize on 386/486 1: - movw %cx, %ds - movw %cx, %es - movw %cx, %fs - movw %cx, %gs - movw %cx, %ss - - # Jump to the 32-bit entrypoint + # Transition to 32-bit mode .byte 0x66, 0xea # ljmpl opcode -2: .long 0 # offset +2: .long in_pm32 # offset .word __BOOT_CS # segment .size protected_mode_jump, .-protected_mode_jump + + .code32 + .type in_pm32, @function +in_pm32: + # Set up data segments for flat 32-bit mode + movl %ecx, %ds + movl %ecx, %es + movl %ecx, %fs + movl %ecx, %gs + movl %ecx, %ss + # The 32-bit code sets up its own stack, but this way we do have + # a valid stack if some debugging hack wants to use it. + addl %ebx, %esp + + # Clear registers to allow for future extensions to the + # 32-bit boot protocol + xorl %ecx, %ecx + xorl %edx, %edx + xorl %ebx, %ebx + xorl %ebp, %ebp + xorl %edi, %edi + + jmpl *%eax # Jump to the 32-bit entrypoint + + .size in_pm32, .-in_pm32 |